PROCESS MONITOR FOR A WELD CONTROLLER

A weld controller maintains an internal dynamic model of load impedance, whi ch tracks normal impedance variations that occur as the weld tooling degrades. The weld controller contains a weld process monitor function that tests an estimated load impedance of a weld schedule presently under execution against an internal dynamic model an d generates events when characteristics of the estimated load impedance of the present weld falls outside an operator definable band, indicating a problem with the workpiece presently being welded. The weld controller further includes the capability to accept a static model of the load impedance that is used as the reference impedance for the weld control and tooling. The weld controller also includes means to declare an event when characteristics of the dynamic model differ from the static model by an operator-defined amount. The weld controller allows a distinction to be made between a short-term difference in load impedance, generally indicative of a weld process variati on and the long-term difference in load impedance, generally indicative of tooling degradation. This provides for tighter controls of wel d process variations than could previously be achieved, coupled with an indication of incipient tooling faults.